Binary prefix: Binary prefix, Bit, Byte, Computer memory, SI prefix, Serial communication, Transmission medium, National Institute of Standards and Technology, ... Electrotechnical Commission, IEC 60027

In computing, a binary prefix is a set of letters that precede a unit of digital quantity (bit and byte) to indicate multiplication by a power of two. In certain contexts in computing, such as computer memory size, the units bit and byte have traditionally been reported in multiples of powers of two. The term binary prefix is intended to differentiate usage of the multiple's names and symbols (for example, kilo or k) from the SI prefixes, which are always decimal (power of 10) multiples. The first few binary multipliers, e.g., 1024 (210), 1048576 (220), are close in value to SI prefixes, such as kilo (1000 = 103) and mega (1000000 = 106), respectively. Therefore it became common practice amongst computer professionals to use these prefixes for the binary multiples, for example, to use the symbol M (mega) to mean 1048576 instead of 1000000. However, when used with SI units and in some other contexts, these prefixes retained their decimal meanings. Certain disciplines of computing have always used these prefixes as decimal multipliers, for example, when specifying quantities of bits transmitted on a serial transmission medium.